The present invention relates to the use of a catalytic system comprising a metal of group VIII, a metal of group VI, a metal oxide as carrier and suitable quantities of a component selected from a, zeolite of the FER type, phosphorous, and a mixture thereof, in upgrading of hydrocarbons boiling in the naphtha range containing sulfur impurities, namely in hydrodesulfurization with contemporaneous skeleton isomerization of olefins contained in said hydrocarbons and/or with reduction of olefins hydrogenation, carried out in a single step.
This catalytic system can be used in particular for upgrading of hydrocarbons boiling in the naphtha range deriving from cracking processes, preferably of hydrocarbons boiling in the naphtha range derived from FCC (fluid catalytic cracking).
In fact hydrocarbons boiling in the naphtha range from FCC (i.e. gasoline cut )are used as a component in the blending of reformulated gasolines. For this purpose, it must have a high octane number and also a low sulfur content, in compliance with the limits of the law, which are becoming more and more restrictive, to reduce the emission of contaminants. The sulfur present in the gasoline pool in fact mainly derives ( greater than 90%) from the gasoline cut deriving from FCC. This cut is also rich in olefins which have a high octane number. Hydrogenation processes suitable for desulfurizing also result in the hydrogenation of the olefins present and consequently cause a considerable reduction in the octane number (RON and MON). The necessity has therefore been felt for identifying a catalytic system which, combined with suitable hydrodesulfurization conditions, diminishes the sulfur in the hydrocarbons boiling in the naphtha range and at the same time reduces to the minimum the deterioration in the octane qualities (RON), which can be achieved for example by the skeleton isomerization of olefins present and/or by the inhibition of hydrogenation of olefins double bond.
The use of zeolites with medium pores as isomerization catalysts and the consequent octane recovery of loadings previously subjected to desulfurization, are already known (U.S. Pat. No. 5,298,150, U.S. Pat. No. 5,320,742, U.S. Pat. No. 5,326,462, U.S. Pat. No. 5,318,690, U.S. Pat. No. 5,360,532, U.S. Pat. No. 5,500,108, U.S. Pat. No. 5,510,016, U.S. Pat. No. 5,554,274, U.S. Pat. No. 5,599,439). For these processes, to obtain hydrodesulfurization with a reduced octane loss, it is necessary to operate in two steps using specific catalysts and reactors.
U.S. Pat. No. 5,378,352 describes a process in a single step for desulfurizing hydrocarbon fractions which boil within the range of gasolines by means of a catalyst comprising a metal of group VIII, a metal of group VI, a zeolite having a Constraint Index ranging from 1 to 12, and a metal oxide as a binder, at a process temperature which is preferably higher than 340xc2x0 C. Suitable zeolites which can be used in this invention are the following: ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, MCM-22 and mordenite. The use of MCM-22 is indicated as being particularly preferred. In the example a catalyst containing MCM-22 in a high percentage with respect to the total weight of the catalyst (54 wt %) is used and the example relates to xe2x80x9cheavy naphthaxe2x80x9d, a feed cut from FCC gasoline with a high S content, but poor in olefins and consequently not particularly subject to reduction in the octane number as a result of hydrogenation. The suitable process conditions are: temperature higher than; 340xc2x0 C., pressure about 4 to 100 atm, LHSV 0.5 to 10 hxe2x88x921, ratio between hydrogen and the hydrocarbon feed comprised between 93 and 940 std 1/1.
Catalytic materials containing metals of groups VI and VIII, a refractory carrier and a zeolite, for example ZSM-35, are described in EP 442159, EP 437877, EP 434123, for the isomerization and disproportionation of olefins; in U.S. Pat. No. 4,343,692 for hydrodewaxing, in U.S. Pat. No. 4,519,900, for hydrodenitrogenation, in EP 072220, for a two-step process comprising dewaxing and hydrodesulfurization; in U.S. Pat. No. 4,959,140 for a two-step hydrocracking process.
In addition a catalyst is known consisting of Co, 3.5% wt, Mo, 12.8% wt, alumina, 69.8% wt, and P, 2.84% wt, used for deep desulfuration of distillates.
Materials consisting of Mo, Co, alumina and zedlites of the MFI type combined with elements of group IIIA and VIB and also containing phosphorous are described in U.S. Pat. No. 5,576,256.
We have now unexpectedly found that it is possible to desulfurize hydrocarbons boiling in the naphtha range such as full range gasolines containing sulfur and olefins, deriving for example from FCC, with high conversion values, also at lower temperatures and pressures than those preferably used in the prior art, with contemporaneous skeleton isomerization of olefins and/or with very low extent of hydrogenation of olefins double bond, by means of a catalyst comprising a metal of group VIII, a metal of group VI, a metal oxide as carrier and suitable quantities of a component selected from a zeolite of the FER type, phosphorous and mixture thereof. The skeleton isomerization of olefins and/or the very low extent of hydrogenation of olefins double bond allow to obtain desulfurization of hydrocarbon boiling in the naphtha range with very low losses of RON (research octane number) and MON (motor octane number).
These results are not only obtained in the desulfurization of hydrocarbon cuts which boil within the range of xe2x80x9cheavy naphthaxe2x80x9d (130xc2x0-250xc2x0 C.), i.e. cuts poor in olefins, but also in the case of xe2x80x9cfull range naphthaxe2x80x9d feeds which boil within the, range of 35xc2x0-250xc2x0 C., i.e. in the case of cuts rich in olefins.
A first object of the present invention therefore relates to a process for desulfurizing hydrocarbons which boil within the range of 35xc2x0 to 250xc2x0 C., containing olefins and more than 150 ppm of sulfur, with possible skeleton isomerization of olefins, using a catalyst which comprises a metal of group VIII, a metal of group VI, a metal oxide as carrier and a component A selected from:
a) zeolite belonging to the FER type, in a quantity ranging from 5 to 30% by weight with respect to the total weight of the catalyst,
b) phosphorous in a quantity ranging from 0.1 to 10% weight, preferably from 1 to 5% wt, with respect to the total weight of the catalyst,
c) mixtures thereof,
where when the component A is only phosphorous either the catalyst is obtained by impregnation of the metal oxide carrier with an aqueous solution of H3PO4 followed by impregnation with an aqueous solution of the metal of group VIII and an aqueous solution of the metal of group VI, or the catalyst is obtained by drying and calcination of a gel obtained mixing an alcohol dispersion containing a soluble salt of the metal of group VIII and an organic source of aluminum with an aqueous solution containing a soluble salt of the metal of group VI and H3PO4, or the catalyst is obtained by impregnation with an aqueous solution of H3PO4 of a gel, dried and calcined, obtained mixing an alcohol dispersion containing a soluble salt of the metal of group VIII and an organic source of aluminum with an aqueous solution containing a soluble salt of the metal of group VI.
The weight percentage of phosphorous refers to contents expressed as elemental phosphorous; in the final catalyst phosphorous is in form of oxide.
When the catalyst contains a zeolite of the FER type, this zeolite is present in a much lower quantity than that contained in the catalysts used in U.S. Pat. No. 5,378,352. Using this catalytic system characterized by a low content of FER zeolite, excellent desulfurization conversions are obtained, with contemporaneous skeleton isomerization of olefins, even at temperatures which are not high, at which there are lower losses of RON and MON than those caused by the same FER zeolites when used at quantities as high as those used in U.S. Pat. No. 5,378,352 both in the conditions of said patent and in the conditions selected in the present invention.
When the catalyst used in process of the present invention contains only phosphorous as component A, and is prepared by one of the three above described methods, it is possible to desulfurize the hydrocarbons and, at the same time, to have the advantage that the undesired side process of olefins hydrogenation is particularly reduced.
When the catalyst containing both phosphorous and a zeolite of FER type is used in the process for desulfurizing of the present invention, at the same time, the best results are obtained in isomerization and reduction of hydrogenation.
Preferably the catalyst contains, as component A, a zeolite of FER type or mixtures of said zeolite and phosphorous, and therefore a particularly preferred aspect of the invention is a process for desulfurizing hydrocarbons which boil within the range of 35 to 250xc2x0 C., containing olefins and more then 150 ppm of sulfur, with contemporaneous skeleton isomerization of said olefins, using a catalyst which comprises a metal of group VIII, a metal of group VI, a metal oxide as carrier and a component A selected from a zeolite belonging to the FER type, in a quantity ranging from 5 to 30% by weight with respect to the total weight of the catalyst, and mixtures of said zeolite belonging to the FER type, in a quantity ranging from 5 to 30% by weight with respect to the total weight of the catalyst, with phosphorous in a quantity ranging from 0.1 to 10% weight, preferably from 1 to 5% wt, with respect to the total weight of the catalyst.
Preferably the catalysts used in the process of the present invention contain Cobalt and/or Nickel as metal of group VIII, whereas the metal of group VI is preferably selected from molybdenum and/or tungsten. According to a particularly preferred aspect, Co and Mo are used. Preferably the weight percentage of metal of group VIII varies from 1 to 10% with respect to the total weight of the catalyst, more preferably from 2 to 6%, and the weight percentage of metal of group VI preferably varies from 4 to 20% with respect to the total weight of the catalyst, more preferably from 8 to 13. The weight percentages of metal of group VI and metal of group VIII refer to contents of metals expressed as elemental metal of group VI and elemental metal of group VIII; in the final catalyst the metals of groups VI and VIII are in the form of oxides.
According to a particularly preferred aspect, the molar ratio between the metal of group VIII and the metal of group VI is less than or equal to 2, preferably less than or equal to 1.
The metal oxide used as carrier is selected from silica, alumina, silico-aluminas, titania, zirconium and mixtures of thereof. Alumina is preferably used.
When the catalyst contains a zeolite of the FER type, this zeolite can be natural or synthetic, and is selected from Ferrierite, FU-9, ISI-6, Nu-23, Sr-D, ZSM-35. FER structure type is a definition herein used in accordance with Atlas of Zeolite Structure Types, W. M. Meier and D. H. Olson, Butterworths.
Ferrierite is described in P. A. Vaugham, Acta Cryst., 21, 983 (1966), FU-9 is described in EP 55529, ISI-6 in U.S. Pat. No. 4,578,259, Nu-23 in EP 103981, Sr-D is described in Barrer et al., J. Chem. Soc, 1964, 2296.
A particularly preferred aspect of the present invention is that the zeolite ZSM-35 is used. This zeolite is described in U.S. Pat. No. 4,016,245.
Preferably the zeolites are used in acid form, i.e. in the form in which their cation sites are prevalently occupied by hydrogen ions and a particulalry preferred aspect is that at least 80% of the cation sites is occupied by hydrogen ions. Preferably the zeolites in acid form have Si/Al ratio  less than 20.
The catalyst used in the present invention containing zeolite FER as component A, preferably ZSM-35, can be prepared according to the traditional methods. For example by mixing the zeolite with the metal oxide followed by extrusion, calcination, a possible exchange process which reduces the, sodium content, drying, impregnation with a solution containing a salt of a metal of group VI, drying, calcination and impregnation with a solution of a salt of a metal of group VIII, drying and calcination.
A particularly preferred aspect of the process of the present invention is to use a catalyst containing zeolite FER as component A, preferably ZSM-35, prepared by means of the sol-gel technique as follows:
a) an alcohol dispersion is prepared, containing a soluble salt of the metal of group VIII, the zeolite of the FER group and an organic source of aluminum;
b) an aqueous solution is prepared, containing a soluble salt of the metal of group VI and optionally formamide;
c) the alcohol dispersion and the aqueous solution are mixed, obtaining a gel;
d) aging of the gel at a temperature ranging from 10 to 40xc2x0 C.;
e) drying of the gel;
f) calcination of the gel.
In step a) the metal salt of group VIII is for example nitrate, hydroxide, acetate, oxalate and preferably nitrate. The organic source of aluminum is preferably aluminum-trialkoxide having the formula (RO)3Al, wherein R is an alkyl containing from 2 to 6 carbon atoms, and is preferably isopropyl or sec-butyl.
In step b) the soluble salt of the metal of group VI can be acetate, oxalate or ammonium salts. A preferred aspect is to operate in the presence of formamide (Drying Control Chemical Agent) which favours the stabilization of the-porous structure during the drying phase.
The quantities of the reagents are selected in relation to the composition of the final catalyst.
In step c), according to the preferred sequence, the solution from step b) is added to the suspension of step a).
In step d) the so obtained gel is maintained at a temperature from 10xc2x0 to 40xc2x0 C., for a time ranging from 15 to 25 h.
Step e) is carried out at a temperature ranging from 80 to 120xc2x0 C.
Step f) is carried out at a temperature ranging from 400 to 600xc2x0 C.
The catalysts containing zeolite of FER type, as component A, prepared according to the sol-gel method, are new, show the lowest losses of RON and MON comparated with the catalysts having the same composition prepared according to the known techniques and are a further aspect of the present invention.
When a catalyst containing both zeolite and phosphorous is used in the process of the present invention, it can be prepared either using, the above sol-gel procedure where in the step b) the aqueous solution also contains H3PO4, or by impregnation of the catalyst obtained from step f) with an aqueous solution of H3PO4.
Another particularly preferred aspect of the process of the present invention is to use a catalyst with zeolite FER as component A prepared by:
a) impregnation of metal oxide carrier with an aqueous solution of metal of group VIII and an aqueous solution of metal of group VI,
b) drying and calcination of the material resulting from step a),
c) mixing the impregnated metal oxide obtained from step b) with the zeolite of FER type.
The quantities of reagents are selected in relation to the composition of the final catalyst.
The impregnations of step a) are carried out with any conventional method. Between the impregnations a step of drying and calcination can be performed. Before the step c) the impregnated metal oxide can be crushed and sieved in particles of  less than 0.2 mm and then, in step c), mixed with the zeolite by physical mixture or by dispersing the particles in an organic solvent such as cyclohexane or cyclohexanol. The solvent is vaporized and the catalyst particles dried and calcined. The mixing of step c) can be also carried out by mixing and homogenizing a solid mixture comprising the impregnated metal oxide (of particle size  less than 0.2 mm), the zeolite, a binder and optionally combustible organic polymers. The mixture so obtained can be kneaded with a peptizing acid solution, extruded, dried and calcined by any conventional method. Alternatively, the paste can be pelletized, dried and calcined by any conventional method.
When a catalyst containing both zeolite and phosphorous is used in the process of the present invention, it can be prepared using the above mixing procedure where in the step a) the metal oxide carrier is first impregnated with an aqueous solution of H3PO4 and then is impregnated with an aqueous solution of metal of group VIII and an aqueous solution of metal of group VI.
The catalysts which comprise a metal of group VIII, a metal of group VI, a metal oxide as carrier, a zeolite of the FER type, in a quantity ranging from 5 to 30% by weight with respect to the total weight of the catalyst, and phosphorous in a quantity ranging from 0.1 to 10%, preferably from 1 to 5% wt, are new and are another aspect of the present invention.
When the catalyst used in the process of the present invention contains only phosphorous, from 0,1 to 10% by weight with respect to the total weight of the catalyst, preferably from 1 to 5% wt, it is obtained with one of the following methods of preparation:
1) by impregnation of the metal oxide carrier with an aqueous solution of H3PO4 followed by impregnation with an aqueous solution of the metal of group VIII and an aqueous solution of the metal of group VI, or
2) by drying and calcination of a gel obtained mixing an alcohol dispersion containing a soluble salt of the metal of group VIII and an organic source of aluminum with an aqueous solution containing a soluble salt of the metal of group VI and H3PO4, or
3) by impregnation with an aqueous solution of H3PO4 of a gel,dried and calcined, obtained mixing an alcohol dispersion containing a soluble salt of the metal of group VIII and an organic source of aluminum with an aqueous solution containing a soluble salt of the metal of group VI.
In the first preparation the impregnations are carried out with any conventional method. Preferably the metal oxide carrier has a surface area lower than 240 m2/g. Between the impregnation with phosphoric acid and the impregnation with the metals drying and calcination are carried out.
In the second and third preparations, the conditions and quantities of sol-gel technique are used, as those above described in the sol-gel preparation of the catalyst containing zeolite FER as component A.
The catalysts used in the process of the present invention only containing phosphorous as component A, from 0.1 to 10% wt, obtained with one of the above three methods, are new and are another aspect of the present invention.
The catalysts used in the process of the present invention can be used as such or, preferably, extruded according to the known techniques, i.e. using a binder, as pseudobohemite, and a peptizing agent, as acetic acid solution, added to the catalyst to produce an estrudable paste.
In particular when the catalysts are prepared by sol-gel, there is not need to add a binder during the extrusion process.
The hydrodesulfurization process of the present invention is carried out at a temperature ranging from 220 to 340xc2x0 C., preferably from 220 to 330xc2x0 C., at a pressure ranging from 5 to 20 Kg/cm2, at a LHSV ranging from 1 to 10 hxe2x88x921. The hydrogen is used in a quantity ranging from 100 to 500 times with respect to the hydrocarbons present (N1/1). The hydrocarbon mixtures which can be desulfurized according to the process of the present invention contain more than 150 ppm of sulfur. For example hydrocarbon mixtures with a sulfur content higher than 1000 ppm, even higher than 10000 ppm can be subjected to hydrodesulfurization. The hydrocarbon mixture which is preferably subjected to hydrodesulfurization according to the process of the present invention consists of hydrocarbons boiling in the naphtha range deriving from cracking or coking processes. In the following examples catalysts preparations are reported, and upgrading tests either on a model feed or on a full range FCC naphtha.